Is Radiosensitivity Associated to Different Types of Blood Groups? (A cytogenetic study).

Many biological factors affect radiosensitivity. In this study, radiosensitivity among the different blood groups was investigated. Peripheral blood sample of 95 healthy people were divided into two parts. One part was irradiated with 2 Gy Co-60 gamma rays and the second one was considered as control. Then all the samples were studied by cytokinesis-blocked micronucleus assay (CBMN assay). Our study showed that the radiosensitivity index of A+ and O+ groups was significantly higher and lower than other blood groups, respectively. It seems that blood type can be used as a radiosensitivity index for determining the given dose to radiotherapy, although extensive studies are necessary.

adiosensitivity is the relative susceptibleness of cells, tissues, organs or organisms to the dangerous effect of ionizing radiation (1). Inherent characteristic is one of the important reasons of differences in radiation sensitivity (1)(2). The physical specifications of ionizing radiation such as its type (particle or photon), energy and dose rate could alter the biological response of organ or tissue to ionizing radiation (2)(3)(4). Previous studies have confirmed the relationship between genetics and radiosensitivity (5)(6). A recent study has shown that mutations in the ataxia telangiectasia gene (ATM) result in an abnormal p53-mediated cellular response to DNA damage produced by ionizing radiation. Also, the potential role of several identified genes such as BRCA and NBS1, which are involved in the cellular response to radiation induced DNA damage is reported too (6). A clinical study has suggested that a large spectrum of normal tissue reactions may occur among the radiotherapy patients. Because of the difference in the individual radiosensitivity and radiotherapy, the patients who receive identical dose have different normal tissue reactions varying from undetectable to severe (7).
People with higher radiosensitivity, most likely will suffer from deterministic and stochastic effects in radiotherapy (7). The results of the studies have important factor for predicting radiosensitivity in the head and neck cancers (5). It has shown an association between the in vitro radiosensitivity of breast cancer patients and the clinical incidence of late (e.g. fibrosis, telangiectasia) normal tissue reaction to radiotherapy (6). In addition to biological conditions, environmental conditions such as existence of radiosensitizers and radioprotectors undoubtedly affect the biological damage of ionizing radiation. One well-studied example is the presence of oxygen during exposure to ionizing radiation that stabilizes reactions to ionizing radiation and then increases the biological damage of radiation (4). The blood group is an inherent characteristic and its classification is based on the presence or absence of ABO blood group antigens on the surface of red blood cells. The occurrence of some diseases is related to blood type (8) and studies have reported that ABO blood group is an important genetic risk factor for several radiation related illnesses such as pancreatic cancer (9), hepatocellular carcinoma (10), endometrial and cervical cancer (11). In this study, the association between the radiosensitivity and ABO blood group was investigated by cytokinesis-blocked micronucleus assay (CBMN) in a case-control cytogenetic study.

Subjects and sampling
Ten milliliter blood samples of 95 (25 A+, 25 B+, 25 O+ and 20 AB+) non-radiation worker, nonsmoker or alcohol-user healthy donors age between 18-25 years were taken under sterile conditions in the presence of sodium heparin anticoagulant. The samples were divided into two identical values (5ml) which were maintained in similar conditions. The subjects' blood groups, any cancer history in their families and recent radiation exposures were filled in the questionnaire through an interview.

Irradiation
One part of each sample was considered as the control and the second equivalent part was exposed to 2 Gy of gamma rays from a tele-cobalt therapy source (Theratone780, Canada). The dose rate was 120 cGy/min and the source to samples distance (SSD) was 80 cm. The exposed and nonexposed blood samples were transferred to cell culture laboratory for the CBMN assay.

CBMN (cytokinesis blocked micronuclei assay)
CBMN assay was performed on both exposed and control samples as reported by international atomic energy agency (IAEA). In this cytogenetic technique, 0.5 ml of the whole blood was added to  (12)(13). The proportion of MN in exposed to non- Fig. 1. Mean frequency of micronuclei in control and exposed groups of different blood groups. Fig. 2. Radiosensitivity index (RI) of different blood groups. exposed samples in each blood group was considered as its radiosensitivity index (1,3). If one person's cells are more radiosensitive, after taking 2 Gy radiation dose, more DNA breaks (or MNs) occurs and its proportion to non exposed cells will be higher than a person with lower radiosensitivity.

Statistical analysis
The statistical analysis was performed using SPSS 16 by Pair sample t-test between the control and exposed groups and analysis of variance (ANOVA) test between the different blood groups.
The p-value < 0.05 was considered statistically significant.

Results
The mean micronuclei frequencies of the different blood groups were shown in figure 1. As the graphs show, the micronuclei frequency in the exposed samples for all of the blood groups is significantly higher than the control (P <0.001).
Also, there is a significant difference in the micronuclei frequencies of O+ and other blood types in control group (p< 0.001). The difference of micronuclei frequencies between A+ and O+ in exposed groups is significant too (P= 0.015).
The increase in the number of micronuclei after exposure to 2 Gy irradiation for all of the four blood groups are shown in